docs: add required permissions to action README files

Document the specific GitHub permissions needed for each action
based on testing experience to prevent API permission errors.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: vaind

danger/README.md

@@ -25,6 +25,17 @@ jobs:
   * required: false
   * default: `${{ github.token }}`
 
+## Required Permissions
+
+For workflows using this action, you need to set the following permissions:
+
+```yaml
+permissions:
+  contents: read       # To read repository files
+  pull-requests: write # To post comments on pull requests
+  statuses: write      # To post commit status checks
+```
+
 ## Outputs
 
 * `outcome`: Whether the Danger run finished successfully. Possible values are `success`, `failure`, `cancelled`, or `skipped`.

updater/README.md

@@ -104,6 +104,17 @@ jobs:
   * type: string
   * required: true
 
+## Required Permissions
+
+For workflows using this action, you need to set the following permissions:
+
+```yaml
+permissions:
+  contents: write      # To modify files and create commits
+  pull-requests: write # To create and update pull requests
+  actions: write       # To cancel previous workflow runs
+```
+
 ## Outputs
 
 * `prUrl`: The created/updated PR's URL.